This invention pertains generally to electronic counter-measure (ECM) systems and more particularly to an adaptive interferometer for causing errors to be introduced into a tracking radar.
The cost of modern fighter aircraft coupled with the increased effectiveness of ground-to-air missile defense systems has resulted in the development of ECM systems designed to mask such aircraft from ground-based fire control radars. One known type of ECM system designed to protect a penetrating aircraft against a surface-to-air missile which is being guided by a command guidance system is the so-called "Cross-Eye" system. With such a system a portion of the signal transmitted by a control radar, say a ground-based fire control radar, is received at the penetrating aircraft and then is processed to be retransmitted as a pair of equal amplitude, but 180.degree. phase-opposed, signals (referred to hereinafter as the "jamming signals") in the direction of the ground based fire control radar. The magnitude of the jamming signals is sufficient to mask the skin return from a penetrating aircraft so that the ground-based fire control radar is caused to attempt to track on the jamming signals with the final result that unacceptably large tracking errors are engendered and a guided missile in flight toward the penetrating aircraft is misguided.
Generally, an aircraft employing a "Cross-Eye" system has an appropriate transmitting and receiving antenna located on each of its wings. Thus, a receiving antenna located on a first one of the wings is connected, via an amplifier and requisite transmission lines, to a transmitting antenna disposed on the second wing. In like manner, a receiving antenna located on the second wing is connected, via a 180.degree. phase shifter, an amplifier, and requisite transmission lines, to a transmitting antenna located on the first wing.
It will be appreciated by those of skill in the art that the effectiveness of such "Cross-Eye" systems is dependent upon how well the amplitude and phase of the retransmitted signals are controlled. Unfortunately, however, with transmitting and receiving antennas located on opposite wing tips, it is virtually impossible, even in the best of conditions, to provide the required accuracy in phase and amplitude of the retransmitted, or jamming signals. The problem is even more difficult in the severe vibration environment and over temperature extremes often experienced by any aircraft.